Geology Reference
In-Depth Information
apart and then how later the pieces could come back together. His argument was based on
biogeography, the global distribution of plants, animals and fossils, and the supposition that
the presence of tropical fossils at high latitudes could be due to continents moving across
climate zones. Similar types of fossils were found in ancient rocks on continents that have
few modern species in common, which suggested the separation of once connected land-
masses.
Most American geologists did not believe that Earth's crust could withstand the compres-
sional forces required to move continents around. At a 1928 symposium held to debate the
idea of continental drift, one eminent geologist accused Wegener of cherry-picking facts
that supported his idea and ignoring facts and principles opposed to it. Another complained
that for Wegener to be correct geologists would have to “forget everything which has been
continents and ocean basins as ancient features worked well enough so that geologists did
not believe they had to start from scratch in trying to explain earth history.
It took several more decades to develop a valid explanation of just how mountains arose.
The answer was plate tectonics. In fact, the theory of plate tectonics came together to ex-
plain three independent mysteries that only made sense when considered together—high
heat flow over submarine mountain ranges out in the middle of the oceans, a bar-code-
like pattern of magnetic stripes on the seafloor, and the global distribution of earthquakes.
Different groups of scientists working in different places, on different problems, with new
technologies independently discovered the pieces needed to solve the grand puzzle of what
caused continents to move across Earth's surface.
Before sonar, seafloor topography was veiled beneath the waves, essentially unknown
in deep water away from reefs and oceanic islands. The development of sonar opened an
entirely new view of the seafloor. Widely used during the Second World War as a form of
underwater radar to hunt enemy submarines and help better target surface ships, sonar also
could be used to map the depth of the seafloor. The idea behind sonar is simple: bounce
a pulse of sound off something and measure how long it takes for the echo to come back.
Knowing the speed of sound you can then determine the distance to the reflector. The pro-
cess is similar to the navigation method used by bats. When oceanographers began system-
